Solid‐State NMR Characterization of Wilkinson’s Catalyst Immobilized in Mesoporous SBA‐3 Silica

The Wilkinson’s catalyst [RhCl(PPh₃)₃] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA‐3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid‐state NMR methods. The successful modification of the silica surface was confirmed by ²⁹Si CP‐MAS NMR experiments. The presence of the T_n peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. ³¹P‐³¹P J‐resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable ³¹P‐³¹P J‐coupling, well resolvable in 2D MAS NMR experiments. This J‐coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable ³¹P‐³¹P J‐coupling in off‐magic‐angle‐spinning experiments, as well as slow‐spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules.     

Magnetically water‐dispersible and recoverable rhodium organometallic catalyst derived from Wilkinson's catalyst for promoting organic reactions

A novel magnetic rhodium catalyst was prepared through immobilizing Wilkinson's catalyst on the surface of silica‐coated iron oxide nanoparticles. After (thio)diphenylphosphine (─S&─PPh₂) was modified on the surface of the silica‐coated iron oxide nanoparticles, tris(triphenylphosphine)rhodium(I) chloride was employed to synthesize the Rh(Cl)(PPh₃)₂(Ph₂P&─S&─) complex, affording a rhodium loading of 0.16 mmol g⁻¹. The Rh(I) organometallic magnetic nanoparticles form a novel class of heterogeneous catalyst which is particularly suitable for the practice of organic synthesis. The prepared system exhibits high catalytic efficiency in Suzuki–Miyaura and Miyaura–Michael reactions in ethanol–water solution. High yield, low reaction times, use of green solvents and non‐toxicity of the catalyst are the main merits of this protocol. Also, magnetic separation is an environmentally friendly alternative for the recovery of the catalyst, since it minimizes energy and catalyst loss by preventing mass loss and oxidation. The produced catalyst was characterized using a variety of techniques.     

Enantioselective Divergent Synthesis of (−)‐cis‐α‐ and (−)‐cis‐γ‐Irone by Using Wilkinson’s Catalyst

A simple, efficient synthesis is reported for (?)‐cis‐α‐ and (?)‐cis‐γ‐irone, two precious constituents of iris oils, in ≥99 % diastereomeric and enantioselective ratios. The two routes diverge from a common intermediate prepared from (?)‐epoxygeraniol. Of general interest in this approach is the installation of the enone moiety of irones through a NHC?Au^I‐catalyzed Meyer–Schuster‐like rearrangement of a propargylic benzoate and the use of Wilkinson’s catalyst for the stereoselective hydrogenation of a prostereogenic exocyclic double bond to secure the critical cis stereochemistry of the alkyl groups at C2 and C6 of the irones. The stereochemical aspects of this reaction are rationally supported by DFT calculation of the conformers of the substrates undergoing the hydrogenation and by a modeling study of the geometry of the rhodium η² complexes involved in the diastereodifferentiation of the double bond faces. Thus, computational investigation of the η² intermediates formed in the catalytic cycle of prostereogenic alkene hydrogenation by using Wilkinson’s catalyst could be highly predictive of the stereochemistry of the products.     

Infrared Spectroscopy of a Wilkinson Catalyst in a Room‐Temperature Ionic Liquid

Homogeneous catalysis in room‐temperature ionic liquids (ILs) constitutes a most interesting field of research with high potential in technical applications. As concerns the hydrogenation of unsaturated hydrocarbons, Wilkinson’s compound RhCl(PPh₃)₃ represents a catalyst that provides high selectivity and activity. Herein, we demonstrate the application of infrared spectroscopy to the quantitative analysis of the Wilkinson catalyst in the IL 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). Our study demonstrates for the first time the quantitative, accurate and reproducible determination of the concentration of a rhodium catalyst by means of IR spectroscopy and, moreover, allows the investigation of intermolecular interactions. Spectral features, located mainly in the fingerprint region of the IR spectrum, are identified revealing the influence of the dissolved catalyst on the IL’s vibrational structure. In particular, the ring‐bending mode of the imidazolium ring shows a frequency shift as a function of catalyst concentration, probably due to hydrogen‐bond formation between the IL cation and the Rh complex. The results show the potential of IR spectroscopy both for application as a quick process control technology in catalytic processes and as a tool for better understanding of IL–catalyst interactions.     

Air‐tolerantly surface‐initiated AGET ATRP mediated by iron catalyst from silica nanoparticles

Well‐defined polymer‐nanoparticle hybrids were prepared by a newly reported method: atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst. The kinetics of the surface‐initiated AGET ATRP of methyl methacrylate from the silica nanoparticles, which was mediated by FeCl₃/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N‐dimethylformamide as the solvent in the presence of a “sacrificial” (free) initiator, was studied. Both the free and grafted polymers were grown in a control manner. The chemical composition of the nanocomposites was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Thermogravimetric analysis was used to estimate the content of the grafted organic compound, and transmission electron micrographs was used to observe the core‐shell structure of the hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2006–2015, 2010     

Enzyme‐Responsive Intracellular‐Controlled Release Using Silica Mesoporous Nanoparticles Capped with ε‐Poly‐L‐lysine

The synthesis and characterization of two new capped silica mesoporous nanoparticles for controlled delivery purposes are described. Capped hybrid systems consist of MCM‐41 nanoparticles functionalized on the outer surface with polymer ε‐poly‐L ‐lysine by two different anchoring strategies. In both cases, nanoparticles were loaded with model dye molecule [Ru(bipy)₃]²⁺. An anchoring strategy involved the random formation of urea bonds by the treatment of propyl isocyanate‐functionalized MCM‐41 nanoparticles with the lysine amino groups located on the ε‐poly‐L ‐lysine backbone (solid Ru‐rLys‐S1 ). The second strategy involved a specific attachment through the carboxyl terminus of the polypeptide with azidopropyl‐functionalized MCM‐41 nanoparticles (solid Ru‐tLys‐S1 ). Once synthesized, both nanoparticles showed a nearly zero cargo release in water due to the coverage of the nanoparticle surface by polymer ε‐poly‐L ‐lysine. In contrast, a remarkable payload delivery was observed in the presence of proteases due to the hydrolysis of the polymer’s amide bonds. Once chemically characterized, studies of the viability and the lysosomal enzyme‐controlled release of the dye in intracellular media were carried out. Finally, the possibility of using these materials as drug‐delivery systems was tested by preparing the corresponding ε‐poly‐L ‐lysine capped mesoporous silica nanoparticles loaded with cytotoxic drug camptothecin (CPT), CPT‐rLys‐S1 and CPT‐tLys‐S1 . Cellular uptake and cell‐death induction were studied. The efficiency of both nanoparticles as new potential platforms for cancer treatment was demonstrated.     

Investigation of catalyst‐transfer condensation polymerization for the synthesis of n‐type π‐conjugated polymer,poly(2‐dioxaalkylpyridine‐3,6‐diyl)

Kumada‐Tamao coupling polymerization of 6‐bromo‐3‐chloromagnesio‐2‐(3‐(2‐methoxyethoxy)propyl)pyridine 1 with a Ni catalyst and Suzuki‐Miyaura coupling polymerization of boronic ester monomer 2 , which has the same substituted pyridine structure, with ^tBu₃PPd(o‐tolyl)Br were investigated for the synthesis of a well‐defined n‐type π‐conjugated polymer. We first carried out a model reaction of 2,5‐dibromopyridine with 0.5 equivalent of phenylmagnesium chloride in the presence of Ni(dppp)Cl₂ and then observed exclusive formation of 2,5‐diphenylpyridine, indicating that successive coupling reaction took place via intramolecular transfer of Ni(0) catalyst on the pyridine ring. Then, we examined the Kumada‐Tamao polymerization of 1 and found that it proceeded homogeneously to afford soluble, regioregular head‐to‐tail poly(pyridine‐2,5‐diyl), poly(3‐(2‐(2‐(methoxyethoxy)propyl)pyridine) (PMEPPy). However, the molecular weight distribution of the polymers obtained with several Ni and Pd catalysts was very broad, and the matrix‐assisted laser desorption ionization time‐of‐flight mass spectra showed that the polymer had Br/Br and Br/H end groups, implying that the catalyst‐transfer polymerization is accompanied with disproportionation. Suzuki‐Miyaura polymerization of 2 with ^tBu₃PPd(o‐tolyl)Br also afforded PMEPPy with a broad molecular weight distribution, and the tolyl/tolyl‐ended polymer was a major product, again indicating the occurrence of disproportionation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and polymerization of (E)‐p‐[(p‐methoxyphenyl)‐2‐ethenyl]phenylacetylene with Ziegler–Natta,rhodium, and palladium complexes

The synthesis and polymerization of (E)‐p‐[(p‐methoxyphenyl)‐2‐ethenyl]phenylacetylene was carried out with a homogeneous vanadium acetylacetonate/aluminum triethyl catalyst system, a bis(rhodium chloride cycloocta‐1,5‐diene) complex, and a palladium/trimethylsilyl complex. In all cases, the main fraction was a polymer with a stereoregular structure. The polymerization with the vanadium catalyst gave a polymer fraction in a low yield. The polymerization of (E)‐p‐[(p‐methoxyphenyl)‐2‐ethenyl]phenylacetylene with the soluble rhodium complex gave a polymer in a high yield. The soluble palladium/chlorotrimethylsilane complex gave a polymer in a good yield. On the basis of the spectroscopic data, the poly{(E)‐p‐[(p‐methoxyphenyl)‐2‐ethenyl]phenylacetylene)} obtained, in all cases, showed a cis–transoidal stereoregular structure. The molecular mass of poly{(E)‐p‐[(p‐methoxyphenyl)‐2‐ethenyl]phenylacetylene)} was determined by the matrix‐assisted laser desorption/ionization time‐of‐flight technique. The kinetics of the reaction were analyzed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6438–6444, 2005     

Fe3O4‐SAHPG‐Pd0 nanoparticles: A ligand‐free and low Pd loading quasiheterogeneous catalyst active for mild Suzuki–Miyaura coupling and C?H activation of pyrimidine cores

This paper reports a green magnetic quasiheterogeneous efficient palladium catalyst in which Pd⁰ nanoparticles have been immobilized in self‐assembled hyperbranched polyglycidole (SAHPG)‐coated magnetic Fe₃O₄ nanoparticles (Fe₃O₄‐SAHPG‐Pd⁰). This catalyst has been used for effective ligandless Pd catalyzed Suzuki–Miyaura coupling reactions of different aryl halides with substituted boronic acids at room temperature and in aqueous media. Herein, SAHPG is used as support; it also acts as a reducing agent and stabilizer to promote the transformation of Pd^II to Pd⁰ nanoparticles. Also, this environmental friendly quasiheterogeneous catalyst is employed for the first time in the synthesis of new pyrimido[4,5‐b]indoles via oxidative addition/C? H activation reactions on the pyrimidine rings, which were obtained with higher yield and faster than when Pd(OAc)₂ was used as the catalyst. Interestingly, the above‐mentioned catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled several times with no significant decrease in the catalytic activity.     

Self‐assembly of N‐carboxyethylchitosan near the isoelectric point

For the first time the possibility to obtain nanostructures by self‐assembly of chitosan polyampholytic derivative was demonstrated. The self‐assembly of N‐carboxyethylchitosan (CECh) took place only near its isoelectric point (pH 5.0–5.6). Out of the pH range 5.0–5.6, CECh aqueous solutions behaved as real solutions. Dynamic light scattering and atomic force microscopy analyses revealed that spherically shaped or rod/worm‐like nanosized assemblies were formed depending on the polymer molar mass, pH value, and polymer concentration. CECh of two different molar masses was studied in concentrations ranging from 0.01 to 0.1 mg/mL. The structures from CECh of weight‐average molar mass (M_w ) 4.5 × 10³ g/mol were spherical regardless the pH and polymer concentration. In contrast, CECh of high molar mass (HMMCECh, M_w = 6.7 × 10⁵ g/mol) formed self‐assemblies with spherical shape only at pH 5.0 and 5.6. At pH 5.2 spherical nanoparticles were obtained only at polymer concentration 0.01 mg/mL. The mean hydrodynamic diameter (D_h) of the obtained nanoparticles was in the range from 30 to 980 nm. On increasing the concentration, aggregation of the nanoparticles appeared, and at HMMCECh concentration 0.1 mg/mL, rod/worm‐like structures were obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6712–6721, 2008     

Synthesis of star‐shaped poly(D,L‐lactic acid‐alt‐glycolic acid)‐b‐poly(L‐lactic acid) with the poly(D,L‐lactic acid‐alt‐glycolic acid) macroinitiator and stannous octoate catalyst

Two types of three‐arm and four‐arm, star‐shaped poly(D,L ‐lactic acid‐alt‐glycolic acid)‐b‐poly(L ‐lactic acid) (D,L ‐PLGA50‐b‐PLLA) were successfully synthesized via the sequential ring‐opening polymerization of D,L ‐3‐methylglycolide (MG) and L ‐lactide (L ‐LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct₂) as a catalyst. Star‐shaped, hydroxy‐terminated poly(D,L ‐lactic acid‐alt‐glycolic acid) (D,L ‐PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization of L ‐LA with the SnOct₂ catalyst in bulk at 130 °C. For the polymerization of L ‐LA with the three‐arm, star‐shaped D,L ‐PLGA50 macroinitiator (number‐average molecular weight = 6800) and the SnOct₂ catalyst, the molecular weight of the resulting D,L ‐PLGA50‐b‐PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) of L ‐LA to MG, and the molecular weight distribution was rather narrow (weight‐average molecular weight/number‐average molecular weight = 1.09–1.15). The ¹H NMR spectrum of the D,L ‐PLGA50‐b‐PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio of L ‐LA to the macroinitiator. The ¹³C NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L ‐PLGA50 as the first block and poly(L ‐lactic acid) as the second block. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 409–415, 2002     

Synthesis and characterization of a novel soluble reactive ladder‐like polysilsesquioxane with side‐chain 2‐(4‐chloromethyl phenyl) ethyl groups

A new kind of soluble structure‐ordered ladder‐like polysilsesquioxane with reactive side‐chain 2‐(4‐chloromethyl phenyl) ethyl groups ( L ) was first synthesized by stepwise coupling polymerization. The monomer, 2‐(4‐chloromethyl phenyl) ethyltrichlorosilane ( M ), was synthesized successfully by hydrosilylation reaction with dicyclopentadienylplatinum(II) chloride (Cp₂PtCl₂) ­catalyst. Monomer and polymer structures were characterized by FT‐IR, ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapor pressure osmometry (VPO) and X‐ray diffraction (XRD). This novel reactive ladder‐like polymer has promise potential applications as initiator for atom transfer radical polymerization, and as precursor for a variety of advanced functional polymers. Copyright © 2001 John Wiley & Sons, Ltd.     

Irreversible helix rearrangement from Cis‐transoid to Cis‐cisoid in poly(p‐n‐hexyloxyphenylacetylene) induced by heat‐treatment in solid phase

Polymerization of p‐n‐hexyloxyphenylacetylene (pHPA) by using a [Rh(norbornadine)Cl]₂‐triethylamine catalyst was carried out at room temperature to afford stereoregular helical poly(p‐n‐hexyloxyphenylacetylene)s (PpHPAs). When ethanol and n‐hexane were used as polymerization solvents, a bright yellow PpHPAs, poly( Y ) with M_n = 8.5 × 10⁴ and its purple red polymer, poly( R ) with M_n = 5.3 × 10⁴ were obtained in 95% yields and 84% yields, respectively. Diffuse reflective UV–vis spectra of poly( Y ) and poly( R ) in solid phase showed different broad absorption peaks at 445 and 575 nm, respectively. X‐Ray diffraction patterns of poly( Y ) and poly( R ) showed typical columnar structures assignable to cis‐transoid and cis‐cisoid structures, respectively, which were also supported by molecule mechanics calculation. Poly( Y ) was irreversibly transformed to a reddish‐black polymer, poly( Y‐B ), which columnar diameter was nearly the same as that of poly( R ). Further, poly( Y ) showed an exothermic peak in the differential scanning calorimetry trace at 80 °C for 1 h in N₂ gas. Thus, these findings suggest a thermally irreversible rearrangement from an unstable cis‐transoid form, poly( Y ) with a stretched cis‐transoid helix to a stable cis‐cisoid form, poly( R ), with a contracted cis‐cisoid helix in the solid phase to give poly( Y → B ) with the cis‐cisoid form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Use of the Wilkinson Catalyst for the ortho‐CH Heteroarylation of Aromatic Amines: Facile Access to Highly Extended π‐Conjugated Heteroacenes for Organic Semiconductors

An unprecedented catalytic system composed of the Wilkinson catalyst [Rh(PPh₃)₃Cl] and CF₃COOH enabled the highly regioselective cross‐coupling of aromatic amines with a variety of heteroarenes through dual C? H bond cleavage. This protocol provided a facile and rapid route from readily available substrates to (2‐aminophenyl)heteroaryl compounds, which may be conveniently transformed into highly extended π‐conjugated heteroacenes. The experimental studies and calculations showed that thianaphtheno[3,2‐b]indoles have large HOMO–LUMO energy gaps and low‐lying HOMO levels, and could therefore potentially be high‐performance organic semiconductors. Herein we report the first use of a rhodium(I) catalyst for oxidative C? H/C? H coupling reactions. The current innovative catalyst system is much less expensive than [RhCp*Cl₂]₂/AgSbF₆ and could open the door for the application of this approach to other types of C? H activation processes.     

Magnetic molecularly imprinted composite for the selective solid‐phase extraction of p‐aminosalicylic acid followed by high‐performance liquid chromatography with ultraviolet detection

A new method for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples has been developed using magnetic molecularly imprinted polymer nanoparticles before determination by high‐performance liquid chromatography. The Fe₃O₄ nanoparticles were first prepared through the chemical coprecipitation of Fe²⁺ and Fe³⁺ and then coated with a vinyl shell. Subsequently, a layer of molecularly imprinted polymers was grafted onto the vinyl‐modified magnetic nanoparticles by precipitation polymerization. FTIR spectroscopy, scanning electron microscopy, vibrating sample magnetometry, and thermogravimetric analysis were applied to characterize the sorbent properties. Moreover, the predominant parameters affecting the magnetic solid phase extraction such as sample pH, sorption and elution times, the amount of sorbent, and composition and volume of eluent were investigated thoroughly. The maximum sorption capacity of the imprinted polymer toward p‐aminosalicylic acid was 70.9 mg/g, which is 4.5 times higher than that of the magnetic nonimprinted polymer. The magnetic molecularly imprinted polymer nanoparticles were applied for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples and satisfactory results were achieved. The results illustrate that magnetic molecularly imprinted polymer nanoparticles have a great potential in the extraction of p‐aminosalicylic acid from environmental and biological matrices.     

Ring‐opening metathesis polymerization of cis‐cyanocyclooct‐4‐ene: Search for active catalysts,variation of monomer to catalyst ratios and monomer concentrations

The ring‐opening metathesis polymerization (ROMP) of cis‐cyanocyclooct‐4‐ene initiated by ruthenium‐based catalysts of the first, second, and third generation was studied. For the polymerization with the second generation Grubbs catalyst [RuCl₂(?CHPh)(H₂IMes)(PCy₃)] (H₂IMes = N,N′‐bis(mesityl)‐4,5‐dihydroimidazol‐2‐ylidene), the critical monomer concentration at which polymerization occurs was determined, and variation of monomer to catalyst ratios was performed. For this catalyst, ROMP of cis‐cyanocyclooct‐4‐ene did not show the features of a living polymerization as M_n did not linearly increase with increasing monomer conversion. As a consequence of slow initiation rates and intramolecular polymer degradation, molar masses passed through a maximum during the course of the polymerization. With third generation ruthenium catalysts (which contain 3‐bromo or 2‐methylpyridine ligands), polymerization proceeded rapidly, and degradation reactions could not be observed. Contrary to ruthenium‐based catalysts of the second and third generation, a catalyst of the first generation was not able to polymerize cis‐cyanocyclooct‐4‐ene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Multicomponent Transformation of Isoindoline‐1,3‐diimine (=1H‐Isoindole‐1,3(2H)‐diimine), Acetylenic Esters,and Triphenylphosphine to Novel Dihydropyrimido[2,1‐a]isoindole Derivatives

The three‐component reaction of the zwitterions generated from dialkyl acetylenedicarboxylates (=dialkyl but‐2‐ynedioates and triphenylphosphine (Ph₃P) with isoindoline‐1,3‐diimine (=1H‐isoindole‐1,3(2H)‐diimine) is described (Scheme 1). This reaction affords the corresponding special type of substituted dihydropyrimido[2,1‐a]isoindole derivatives in good yields without using any catalyst and activation (Table).     

Use of the Wilkinson Catalyst for the ortho‐C?H Heteroarylation of Aromatic Amines: Facile Access to Highly Extended π‐Conjugated Heteroacenes for Organic Semiconductors

An unprecedented catalytic system composed of the Wilkinson catalyst [Rh(PPh₃)₃Cl] and CF₃COOH enabled the highly regioselective cross‐coupling of aromatic amines with a variety of heteroarenes through dual C H bond cleavage. This protocol provided a facile and rapid route from readily available substrates to (2‐aminophenyl)heteroaryl compounds, which may be conveniently transformed into highly extended π‐conjugated heteroacenes. The experimental studies and calculations showed that thianaphtheno[3,2‐b]indoles have large HOMO–LUMO energy gaps and low‐lying HOMO levels, and could therefore potentially be high‐performance organic semiconductors. Herein we report the first use of a rhodium(I) catalyst for oxidative C H/C H coupling reactions. The current innovative catalyst system is much less expensive than [RhCp*Cl₂]₂/AgSbF₆ and could open the door for the application of this approach to other types of C H activation processes.     

A new nano‐Fe3O4‐supported organocatalyst based on 3,4‐dihydroxypyridine: an efficient heterogeneous nanocatalyst for one‐pot synthesis of pyrazolo[3,4‐b]pyridines and pyrano[2,3‐d]pyrimidines

A simple and practical strategy for the synthesis of a novel nano‐Fe₃O₄‐supported organocatalyst system based on 3,4‐dihydroxypyridine (Fe₃O₄/Py) has been developed. The prepared catalyst was characterized using Fourier transform infrared spectroscopy, transmission and scanning electron microscopies, X‐ray diffraction, vibrating sample magnetometry and energy‐dispersive X‐ray analysis. Accordingly, the Fe₃O₄/Py nanoparticles show a superparamagnetic property with a saturation magnetization of 61 emu g^?1, indicating potential application in magnetic separation technology. Our experimental results reveal that the pyridine‐functionalized Fe₃O₄ nanoparticles are an efficient base catalyst for the domino condensation of various aromatic aldehydes, Meldrum's acid and 5‐methylpyrazol‐3‐amine under very mild reaction condition and in the presence of ethanol solvent. Moreover, the synthesized catalyst was used for one‐pot, three‐component condensation of aromatic aldehydes with barbituric acid and malononitrile to produce 7‐amino‐2,4‐dioxo‐5‐phenyl‐2,3,4,5‐tetrahydro‐1H‐pyrano[2,3‐d]pyrimidine‐6‐carbonitriles. All reactions are completed in short times and all products are obtained in good to excellent yields. Also, notably, the catalyst was reused five times without significant degradation in catalytic activity and performance. Copyright © 2016 John Wiley & Sons, Ltd.     

Copolymerization of poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) with designed molecular structure by a solid‐state polymerization method

Poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) (PVA‐g‐PPDO) with designed molecular structure was synthesized by a solid‐state polymerization. The solid‐state copolymerization was preceded by a graft copolymerization of PDO initiated with PVA as a multifunctional initiator, and Sn (Oct)₂ as a coininitiator/catalyst in a homogeneous molten state. The polymerization temperature was then decreased and the copolymerization was carried out in a solid state. The products prepared by solid‐state polymerization were characterized by ¹H NMR and DSC, and were compared with those synthesized in the homogeneous molten state. The degree of polymerization (D_p), degree of substitution (D_s), yield and the average molecular weight of the graft copolymer with different molecular structure were calculated from the ¹H NMR spectra. The results show that the crystallization process during the solid‐state polymerization may suppress the undesirable inter‐ or intramolecular side reactions, then resulting in a controlled molecular structure of PVA‐g‐PPDO. The results of DSC measurement show that the molecular structures determine the thermal behavior of the PVA‐g‐PPDO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3083–3091, 2006